Fluidic cavities for on-chip layering and sealing of separation arrays

ABSTRACT

A method for fabricating a fluidic device includes depositing a sacrificial material on a pillar array arranged on a substrate. The method also includes removing a portion of the sacrificial material. The method further includes depositing a sealing layer on the pillar array to form a sealed fluidic cavity.

DOMESTIC PRIORITY

This application is a divisional of U.S. patent application Ser. No.16/274,532, filed Feb. 13, 2019, the disclosure of which is incorporatedby reference herein in its entirety.

BACKGROUND

The present invention generally relates to particle separation arrays.More specifically, the present invention relates to fabrication methodsand resulting structures configured to form fluidic cavities for on-chiplayering and sealing of separation arrays.

There is extensive and growing interest in fluidic technologies such aslab-on-a-chip (LOC). Fluidic technologies provide advantages overtraditional laboratory methods, such as the ability to carry outseparation and detection with high resolution and sensitivity; the needfor only very small quantities of sample and reagent; the relativelysmall footprint of the chip's analytical devices; low manufacturingcost; and short analysis time.

Deterministic lateral displacement (DLD) is a microfluidic LOCtechnology that uses passive pillar arrays to separate particles basedon size. Particles with a size greater than the critical dimension are“bumped” through the pillar array, while particles having a size smallerthan the critical dimension “zigzag” through the array in the directionof fluid flow. The different flow paths, based on size of the particles,enable particle separation. DLD pillar arrays are used in a variety ofapplications, including for example, cell sorting and biosensors.

SUMMARY

Embodiments of the present invention are directed to a method forfabricating a fluidic device. A non-limiting example of the methodincludes depositing a sacrificial material on a pillar array arranged ona substrate. The method also includes removing a portion of thesacrificial material. The method further includes depositing a sealinglayer on the pillar array to form a sealed fluidic cavity.

Another non-limiting example of the method includes depositing asacrificial material on a pillar array arranged on a substrate. Themethod includes depositing an oxide layer on the sacrificial materialand the pillar array. The method includes forming a vent hole in theoxide layer. The method includes flowing a material through the venthole to extract at least a portion of the sacrificial material. Themethod includes depositing a sealing layer on the pillar array to form asealed fluidic cavity.

Embodiments of the present invention are directed to a fluidic device. Anon-limiting example of the fluidic device includes a first pillar arrayarranged on a substrate. The first pillar array includes a plurality ofpillars and a plurality of extraction columns. Each extraction columnincludes an access opening. The fluidic device also includes a sealinglayer arranged on the first pillar array to form a sealed fluidiccavity.

Additional technical features and benefits are realized through thetechniques of the present invention. Embodiments and aspects of theinvention are described in detail herein and are considered a part ofthe claimed subject matter. For a better understanding, refer to thedetailed description and to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The specifics of the exclusive rights described herein are particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other features and advantages ofthe embodiments of the invention are apparent from the followingdetailed description taken in conjunction with the accompanying drawingsin which:

FIG. 1A depicts a DLD array according to embodiments of the presentinvention;

FIG. 1B depicts an enlarged view of the DLD array according toembodiments of the present invention;

FIG. 2 depicts flow through a DLD array according to embodiments of thepresent invention;

FIG. 3 depicts a machine including a DLD array according to embodimentsof the present invention;

FIGS. 4-7 depict a process flow for fabricating a fluidic deviceaccording to embodiments of the present invention, in which:

FIG. 4 depicts a perspective view of the fluidic device, subsequent toforming a pillar array;

FIG. 5 depicts a perspective view of the fluidic device, subsequent todepositing a sacrificial material on the pillar array;

FIG. 6A depicts a perspective view of the fluidic device, subsequent todepositing a second oxide layer, forming vent holes, and partiallyremoving the sacrificial material;

FIG. 6B depicts an enlarged view of a vent hole aligned with anextraction column; and

FIG. 7 depicts a perspective view of the fluidic device, subsequent todepositing a third oxide layer and forming an access hole;

FIG. 8 depicts a perspective view of extraction columns according toembodiments of the present invention;

FIGS. 9A-9E depict a process flow using an extraction column accordingto embodiments of the present invention, in which:

FIG. 9A depicts a perspective view of an extraction column;

FIG. 9B depicts a perspective view of the extraction column, subsequentto depositing a sacrificial material;

FIG. 9C depicts a perspective view of the extraction column, subsequentto depositing an oxide layer and forming a vent hole;

FIG. 9D depicts a perspective view of the extraction column, subsequentto extracting the sacrificial material; and

FIG. 9E depicts a perspective view of the extraction column, subsequentto closing the vent hole;

FIG. 10A depicts an exploded view of a stacked pillar array according toembodiments of the present invention;

FIG. 10B depicts a perspective view of the stacked pillar array of FIG.10A, subsequent to removing the sacrificial material;

FIG. 11A depicts an electron micrograph of a pillar array according toembodiments of the present invention; and

FIG. 11B depicts an electron micrograph of pillar array according toembodiments of the present invention.

The diagrams depicted herein are illustrative. There can be manyvariations to the diagram or the operations described therein withoutdeparting from the spirit of the invention. For instance, the actionscan be performed in a differing order or actions can be added, deletedor modified. Also, the term “coupled” and variations thereof describeshaving a communications path between two elements and does not imply adirect connection between the elements with no interveningelements/connections between them. All of these variations areconsidered a part of the specification.

In the accompanying figures and following detailed description of thedescribed embodiments, the various elements illustrated in the figuresare provided with two or three digit reference numbers. With minorexceptions, the leftmost digit(s) of each reference number correspond tothe figure in which its element is first illustrated.

DETAILED DESCRIPTION

For the sake of brevity, conventional techniques related to DLD arrays(or deterministic lateral displacement (DLD) devices) may or may not bedescribed in detail herein. Moreover, the various tasks and processsteps described herein can be incorporated into a more comprehensiveprocedure or process having additional steps or functionality notdescribed in detail herein. In particular, various steps in themanufacture of DLD arrays are well known and so, in the interest ofbrevity, many conventional steps will only be mentioned briefly hereinor will be omitted entirely without providing the well-known processdetails.

Turning now to an overview of technologies that are more specificallyrelevant to aspects of the invention, LOC technologies, such asmicrofluidic DLD, use small sample quantities. Recovering sortedmaterial from such small volumes can be challenging, particularly whensorted material includes collecting rare biological events. Accordingly,sample volumes sufficient for collection must pass through the chip.

Another challenge for LOC technologies is sealing the fluidic chipsprior to use. The chips must be sealed to protect the device from fluidsand contaminants during downstream processing. Various approaches havebeen used to seal the fluidic cells. For example, poly(dimethylsiloxane)(PMDS), a soft elastomer, has been used to seal the cells. PDMS isoptically transparent and easy to use to create structures using softlithography. Using PDMS, negative patterns can be quickly replicated byspinning the material onto structures patterned in resist, and thencuring, removing, and bonding the material and structures to a targetsubstrate without the need for downstream processing. Despite theseadvantages, PDMS does not have sufficient chemical and thermal stabilityfor some applications, and therefore, it is not compatible with advancedsemiconductor processing techniques that can add further functionalityand scaling, e.g., sorting and detection of nanoscale biologicalmaterial.

Another approach for sealing fluidic chips is glass bonding. Themechanical stability of silicon and glass make them useful in theyounger field of nanofluidics where rigid features precisely controldimensions that are not accessible to PDMS fluidic structures.Additionally, silicon offers a process advantage. Anodic bonding can beused to seal glass to pieces of silicon that have micro/nanofluidicfeatures, without the need for an adhesion layer that can redefine orconstrict fluidics. The glass acts as a ceiling to encapsulate themicro-mechanical silicon elements. Typically, glass bonding to siliconor silicon dioxide occurs through rigorous and labor intensive cleaningand preparation measures. Afterward, pressure is applied to ensure asufficient seal without breaking the glass or silicon. However, anotherchallenge is that fluidic access holes must be drilled into the glasscoverslip to provide an entrance and exit for fluidics flowing into andout of the chip, which is technically challenging on very flat and thinpieces of glass. The size and alignment of these access holes to thechip-level features also limit the level of integration that can beincorporated. Finally, long anneals are typically applied to strengthenthe glass-silicon bond. However, silicon and glass sealing approachescannot be used to manufacture chips on a large scale, and glass sealingcannot be used to integrate complex microelectronics.

Turning now to an overview of the aspects of the invention, one or moreembodiments of the invention address the above-described shortcomings ofthe prior art by providing methods and resulting structures that includefilling fluidic sorting pillar arrays with a sacrificial material (e.g.,polysilicon) that can be subsequently extracted post-fabrication. Anextraction gas (e.g., xenon difluoride, XeF₂) can be used to open themicrofluidic cavities. The microfluidics are also encapsulated in anoxide material, which permits simple preparation and use. Extractioncolumns and vent holes are manufactured into the sortingarrays/microfluidic channels to extract the sacrificial material fromspecific regions of the microfluidic structures, which permits rapidclearing of sacrificial material isolated to the fluidic access portspost-processing. The encapsulated fluidic structures can then be stackedas layers.

The above-described aspects of the invention address the shortcomings ofthe prior art by using filled or partially filled (i.e., filled onlynear the fluidic access ports) fluidic features during fabrication topermit unrestrained processing and cleaning without yield loss to createmultiple layers sealed in an oxide. Encapsulating and stacking fluidicstructures improves volume throughput, thereby aiding in rapid samplecollection, and reducing the manufacturing cost.

Turning now to a more detailed description of aspects of the presentinvention, fluidic devices, for example a pillar sorting array such asDLD array 120 shown in FIG. 1A can be used to separate particles basedon size. The DLD array 120 can be implemented as a configuration ofnanoDLD arrays or microDLD arrays according to some embodiments of thepresent invention. Although DLD array 120 is shown as an exemplaryembodiment of the present invention, it is noted that the describedmethods and devices are not limited to DLD array 120, as they are butone example of a suitable fluidic device. Other fluidic devices,including other devices including sorting pillar arrays, can be used.

FIGS. 1A, 1B, 2, and 3 illustrate how a DLD array 120 and a machine 300including a DLD array 120 are used. FIG. 1A depicts a chip 100 with aDLD array 120, which is a fluidic device, according to embodiments ofthe present invention. FIG. 1B is an enlarged view of the DLD array 120.FIG. 2 is a diagram that depicts how particles and fluid can flowthrough the DLD array 120 in accordance with aspects of the invention.

As best shown in FIG. 1A, the DLD array 120 includes an array of pillars125. The chip 100 has at least one inlet 105A to receive fluidcontaining particles to be separated. The inlet 105A can be an openingor hole in the walls around the DLD array 120 or can span the width ofthe DLD array 120 through which fluid (e.g., water, electrolytesolutions, organic solvents, etc.) and the mixture of particles canflow. In one implementation, there can be two or more inlets 105A and105B. In this case, the inlet 105A receives input of the mixture to besorted, and the mixture can be in a fluid (such as an electrolytesolution). The inlet 105B can be utilized to input a fluid, such as abuffer, not containing the mixture of the particles.

Particles having a size greater than the critical dimension are bumped(i.e., bump mode, see FIG. 2) through the DLD array 120 in the directionof the critical angle α, and fragments larger than the criticaldimension are laterally displaced in the x-axis and collected at outlet140. The critical dimension is the size (e.g., diameter or length) of aparticle that is too large to zigzag through the DLD array 120. On theother hand, particles having a size smaller than the critical dimensionzigzag (i.e., zigzag mode, see also FIG. 2) through the DLD array 120 inthe direction of fluid flow, and these smaller particles are collected(with very little lateral displacement and/or relatively no lateraldisplacement in the x-axis) at the outlet 145. The particles having thesize smaller than the critical dimension follow the direction of thefluid flow, and are sorted through the outlet 145. The outlets 140 and145 can be openings through which the sorted particles can flow and becollected in bins after sorting. It is appreciated that although onlytwo outlets 140 and 145 are depicted, there can more than two outlets toprovide more sorted particles.

The DLD array 120 is a deterministic lateral displacement (DLD) arraywith predefined array parameters. The pillars 125 are periodicallyarranged with spacing λ, and each downstream row (rows run in thex-axis) is offset laterally from the previous row by the amount δbreaking the symmetry of the array. This array axis forms an angleα=tan⁻¹ (δ/=tan⁻¹(ε) with respect to the channel walls 150A, 150B andtherefore the direction of fluid flow. Because of the array asymmetry,fluid flow in the gaps (Gaps) between the posts/pillars G is partitionedinto 1/ε slots. Each of these slots repeats every 1/ε rows so the flowthrough the array is on average straight. Particles transiting the gap Gnear a post can be displaced into an adjacent streamline if theparticle's radius, or effective radius in the case of tumbling oblongobjects such as rods with a defined length, is larger than the slotwidth in the gap. Therefore, larger fragments are deterministicallydisplaced at each post and migrate at an angle α (critical angle) to theflow. Smaller fragments simply follow the streamline paths and flowthrough the array in the direction of fluid flow.

During operation, particles greater than the predefined critical sizeare displaced laterally (in the x-axis) at each row by a pillar 125 andfollow a deterministic path through the array in the so-called “bumping”or “bump” mode (see also FIG. 2). The trajectory of bumping particlesfollows the array axis angle α. Particles smaller than the critical sizefollow the flow streamlines, weaving through the post array in aperiodic “zigzag” mode (see also FIG. 2). Therefore, array elements canbe tailored to direct specific particle sizes at an angle to the flow bybuilding arrays with design parameters shown in FIG. 2, which includeobstacle size/length, spacing between the posts/pillars G, andpost/pillar pitch λ. As noted above, asymmetry is determined by themagnitude of the row-to-row shift δ and is characterized by the slopeε=δ/λ, then leading to the final array angle being λ=tan⁻¹(ε). For agiven array angle, the critical particle size for the bumping mode isdetermined by the ratio between the particle diameter and the pillarspacing and/or gap.

It should be appreciated that the array elements and any ancillaryfluidic channels and reservoirs can be fabricated in silicon wafers byusing standard microfabrication techniques including photolithographyand etching. Arrays can also be molded in polydimethylsiloxane (PDMS) byusing similarly crafted silicon.

FIG. 3 depicts a machine layout of a machine 300 that integrates a DLDchip according to one or more embodiments. The machine 300 can be usedto perform any of the methods described herein that utilize a DLD chipand/or DLD array 120. The machine 300 can include a housing or encasing(not shown) which integrates a DLD chip and any fluidic networks andinjection ports required for transporting fluid samples into and off ofthe DLD chip, as well as injecting/extracting fluid from the housing.The DLD array 120 includes a mixture injection port for injecting thesamples. A syringe pump (not shown), which can be controlled bycontroller 320, can be used to inject the samples and fluids. However,in some embodiments of the invention, the samples also can be manuallyinjected. The DLD array 120 optionally includes another fluid inlet forinjecting fluids. A detector 315 can be attached or mounted to the DLDarray 120 or can be a separate portable unit. The detector 315 can be afull-sized fluorescence microscope for example. The output of thedetector 315 can be fed into the controller 320. In a general operation,a complex mixture of particles is fed into the DLD array 120 through theinjection inlet. The controller 320 can control the sample injection,flow, and/or detector, for example. The controller 320 can include aprocessor that is communicatively connected to an input device, anetwork, a memory, and a display. In some embodiments, the controller320 can include a personal computer, smart phone or tablet devicecommunicatively connected to the fabrication machine 1000.

FIGS. 4-7 depict a process flow for fabricating a fluidic device 400(also referred to as a fluidic device) according to embodiments of thepresent invention. FIG. 4 depicts a perspective view of the fluidicdevice 400, subsequent to forming a pillar array 403 on a substrate 402.The pillar array 403 includes a plurality of pillars 406 that eachinclude an oxide material 404 (also referred to as first oxide layer),for example, silicon dioxide (SiO₂).

According to one or more embodiments of the present invention, thepillars 406 of the pillar array 403 are formed by etching a thick layerof silicon dioxide. The oxide material 404 has a thickness of about 0.5to about 10 micrometers according to some embodiments of the presentinvention. The oxide material 404 has a thickness of about 1 to about 2micrometers according to other embodiments of the present invention.

According to other embodiments of the present invention, pillars 406 ofthe pillar array 403 are etched in silicon, and then a layer of oxide(e.g., silicon dioxide) is grown or deposited on the surface of thesilicon pillars to form a single layer. Non-limiting examples ofmaterials for the substrate 402 include germanium, III-V semiconductors(e.g. GaAs), quartz, or a combination thereof.

Extraction columns 408 are also formed in the oxide material 404, withinthe pillars 406 of the pillar array 403. The extraction columns 408 arestructures that include an access opening 409 within the center of thecolumn. Non-limiting examples of extraction columns 408 are shown inFIG. 8. Each extraction column 408, 408 a, 408 b, 408 c, as shown inFIG. 8, includes one or more access openings 409. The extraction column408 a includes an access opening 409 that includes a single slit withinthe sidewall of the column, which provides unidirectional slit access tothe exterior of the extraction column 408 a. The extraction column 408 bincludes an access opening 409 that includes three slits within thesidewall of the column, which provides tri-directional slit access tothe exterior of the extraction column 408 b. The extraction column 408 cincludes an access opening 409 with four slits within the sidewall ofthe column, which provides quad-directional access to the exterior ofthe extraction column 408 c. The extraction column 408 includes anangled inverted U-shaped structure with an access opening 409 thatincludes a rear-facing (in the direction of fluid flow, see FIG. 2)access opening 409.

Turning again to FIG. 4, each extraction columns 408 of the plurality isarranged at intervals within the pillar array 403. The extractioncolumns 408 are spaced apart with a center-to-center distance (d₁) ofabout 1 to about 50 micrometers according to some embodiments of thepresent invention. According to other embodiments of the presentinvention, the extraction columns 408 are spaced apart with acenter-to-center distance (d₁) of about 10 to about 20 micrometers.

The extraction columns 408 provide structural reinforcement of theceiling by offering pillar 406 support (after the second oxide layer 606is deposited, see FIG. 6A). Each extraction column 408 will also house avent hole 608 (see FIG. 6A) in the center of the column, which will beused to extract the surrounding sacrificial material 505 (see FIG. 5)used to temporarily support the oxide ceiling (second oxide layer 606,see FIG. 6A) during deposition. After the sacrificial material 505 isextracted, ceiling oxide (second oxide layer 606) creates a seal for thenewly formed microfluidic cavity. Centering the vent holes 608 (see FIG.6A) within the extraction columns 408 keeps bubbles and deposited oxideused to close the vent holes 608 isolated internally within the pillars406.

A portion of the oxide layer 404 in an area 410 adjacent to the pillararray 403 is also removed, down to about the level of the base of thepillars 406 of the pillar array 403. The sacrificial material 505subsequently deposited (see FIG. 5) on the pillar array 403 will alsofill the area 410. After the second oxide layer 606 (see FIG. 6A) isdeposited and the sacrificial material 505 is removed (see also FIG.6A), the area 410 filled with the sacrificial material 505 will serve asa plug to seal and protect the newly formed fluidic cavities duringsubsequent processing.

FIG. 5 depicts a perspective view of the fluidic device 400, subsequentto depositing a sacrificial material 505 on the pillar array 403 andwithin the sealing area 410. The sealing area 410 including thesacrificial material 505 will form the access reservoir (also referredto as access port) that prevents wicking of process fluids into thepillar array 403 during the remaining fabrication steps. The sacrificialmaterial 505 is polished back to the surface of the pillar array 403features, such that the pillars 406 and extraction columns 408 areexposed, by for example, chemical mechanical planarization (CMP), toremove topography and to remove material from the surface of the oxidelayer 404. The sacrificial material 505 is, for example, polysiliconaccording to some embodiments of the present invention.

FIG. 6A depicts a perspective view of the fluidic device 400, subsequentto depositing a second oxide layer 606, forming vent holes 608, andpartially removing the sacrificial material 505. The second oxide layer606 can the same or different than the first oxide layer 404. The secondoxide layer 606 is, for example, silicon dioxide. Lithography andetching can be used to form the vent holes 608 in the second oxide layer606. Each vent hole 608 is aligned over the center of an extractioncolumn 408, as shown in the enlarged view 612 in FIG. 6B. The vent holes608 are used to extract the sacrificial material 505 from the pillararray 403. The single layer level extraction process is useful for verylarge area arrays with lateral etching distances, for example, on theorder of millimeter length scales.

The center-to-center distance (d₂) between each of the vent holes 608 isabout 1 to about 50 micrometers according to some embodiments of thepresent invention, which is the same as the center-to-center distance(d₁) as the extraction columns 408 (see FIG. 4). According to otherembodiments of the present invention, the center-to-center distance (d₂)between each of the vent holes 608 is about 10 to about 20 micrometers.

The second oxide layer 606 in which the vent holes 608 are formed has athickness of about 0.5 to about 10 micrometers according to someembodiments of the present invention. The second oxide layer 606 has athickness of about 0.5 to about 2 micrometers according to otherembodiments of the present invention.

The distance (d₃) between the vent hole 608 closest to the sealing area410 which will form the access reservoir is much larger than thedistance (d₂) between the vent holes 608, which enables a plug of thesacrificial material 505 to reliably form in the reservoir that sealsand prevent wicking during subsequent processing. Having a largerdistance (d₃) compared to (d₂) between the vent holes 608 also permitsthe final sacrificial material 505 in the sealing area 410 to be rapidlyextracted in the final stages of processing, instead of slowly removingthe material over a long time.

The distance (d₃) between an edge of a vent hole 608 closest to thesealing area 410 and an edge of the sealing area 410 is about 1 to about50 micrometers according to some embodiments of the present invention.According to other embodiments of the present invention, the distance(d₃) between an edge of a vent hole 608 and an edge of the sealing area410 is about 5 to about 10 micrometers.

As shown in FIG. 6B, the vent hole 608 is aligned with the center of theextraction column 408. Any methods and materials can be used to extractthe sacrificial material 505 from the pillar array 403 area. Anymaterial or etchant, such as a gas such as XeF₂, can be used to extractthe sacrificial material 505 from the pillar array 403. The etchant usedto push the sacrificial material 505 out from within the pillar array403 will follow the flow path 614 indicated by the arrows shown in FIG.6B. The etchant will flow through the vent hole 608 in the second oxidelayer 606 and into the center of the extraction column 408. Thesacrificial material 505 within the extraction column will flow out ofthe extraction column 408. Surrounding sacrificial material 505 aroundthe extraction column 408 and between the pillars 406 of the pillararray 403 to be removed, resulting in formation of a fluidic cavity withopenings 610 between the pillars 406 of the pillar array 403. Thesacrificial material 505 filing the sealing area 410 adjacent to thepillar array 403 is not extracted when the material or etchant is flowedthrough the vent hole 608.

The extraction columns 408 internally house the vent holes 608 tosuppress and contain the impact of the vent holes 608 on the behavior offluidics during operation, e.g., by influencing bubble trapping in thevent holes 608.

FIG. 7 depicts a perspective view of the fluidic device 400, subsequentto depositing a third oxide layer 707 and forming an access hole 708within the third oxide layer 707. The third oxide layer 707 is the sameor different than oxide material layer 404 and second oxide layer 606.The third oxide layer 707 forms a sealing layer that covers and sealsthe vent holes 608 and fluidic cavity within the pillar array 403beneath. The third oxide layer 707 is deposited by, for example, plasmaenhanced chemical vapor deposition (PECVD) which will “pinch off” orclose the vent holes 608.

An access hole 708 is formed in the sealing third oxide layer 707 toprovide access to the sealing area 410 with the sacrificial material 505plug. When the fluidic device 400 is ready for use, the sacrificialmaterial 505 plug is removed from the sealing area 410 through theaccess hole 708.

The access hole 708 is formed in the third oxide layer 707 by, forexample, lithography and etching (e.g., RIE). After forming the accesshole 708, the fluidic device 400 can be diced and cleaned. After finalprocessing and cleaning, the sacrificial material 505 plug is removed byusing an etchant, for example, XeF₂.

FIGS. 9A-9E depict a process flow for forming and using an extractioncolumn according to embodiments of the present invention. FIG. 9Adepicts a perspective view of an extraction column 408 a. The extractioncolumn 408 a is formed in the oxide material 404 and includes an accessopening 409 with a slit to the exterior of the extraction column 408 a.

FIG. 9B depicts a perspective view of the extraction column 408 a,subsequent to depositing a sacrificial material 505 on the extractioncolumn 408 a. The sacrificial material 505 fills the center ofextraction column 408 a within the access opening 409 and surrounds theextraction column 408 a. The sacrificial material 505 is polished backto expose the surface of the extraction column 408 a.

FIG. 9C depicts a perspective view of the extraction column 408 a,subsequent to depositing a second oxide layer 606 and forming a venthole 608 within the second oxide layer 606. The vent hole 608 is alignedwith the access opening 409 in the center of the extraction column 408 abeneath.

FIG. 9D depicts a perspective view of the extraction column 408 a,subsequent to extracting the surrounding sacrificial material 505. Anetchant or other material, for example, XeF₂, is used to extract thesacrificial material 505. The etchant used to push the sacrificialmaterial 505 out from within the extraction column 408 a will follow theflow path 614 indicated by the arrows.

FIG. 9E depicts a perspective view of the extraction column 408 a,subsequent to closing the vent hole 608 by depositing a third oxidelayer 707 on the second oxide layer 606. The third oxide layer 707 isdeposited by, for example, PECVD to seal the microfluidic cavity.

FIG. 10A depicts an exploded view of a stacked pillar array 1000including the sacrificial material 505 according to embodiments of thepresent invention. FIG. 10B depicts a perspective view of the stackedpillar array 1000 of FIG. 10A, subsequent to removing the sacrificialmaterial 505. The above described process flows for forming fluidicdevices can be repeated over two or more layers (first chip 1002 withfirst pillar array and second chip 1003 with second pillar array), whichare then stacked, to linearly improve the volume throughput for a singlechip.

EXAMPLES

FIG. 11A depicts an electron micrograph 1100 of a pillar array 403according to embodiments of the present invention. A pillar array 403was formed in an oxide material 404. Vent holes were formed in an oxidelayer deposited on top of the pillar array 403, and another oxide layer1101 sealed the microfluidic cavity.

FIG. 11B depicts an electron micrograph 1102 of a pillar array 1106according to embodiments of the present invention. FIG. 11B shows across section of a pillar array with a sacrificial polysilicon fill, anoxide layer on top, and with vent holes open, just prior to XeF₂ removalof the polysilicon that leads to FIG. 11A.

Various embodiments of the present invention are described herein withreference to the related drawings. Alternative embodiments can bedevised without departing from the scope of this invention. Althoughvarious connections and positional relationships (e.g., over, below,adjacent, etc.) are set forth between elements in the followingdescription and in the drawings, persons skilled in the art willrecognize that many of the positional relationships described herein areorientation-independent when the described functionality is maintainedeven though the orientation is changed. These connections and/orpositional relationships, unless specified otherwise, can be direct orindirect, and the present invention is not intended to be limiting inthis respect. Accordingly, a coupling of entities can refer to either adirect or an indirect coupling, and a positional relationship betweenentities can be a direct or indirect positional relationship. As anexample of an indirect positional relationship, references in thepresent description to forming layer “A” over layer “B” includesituations in which one or more intermediate layers (e.g., layer “C”) isbetween layer “A” and layer “B” as long as the relevant characteristicsand functionalities of layer “A” and layer “B” are not substantiallychanged by the intermediate layer(s).

The following definitions and abbreviations are to be used for theinterpretation of the claims and the specification. As used herein, theterms “comprises,” “comprising,” “includes,” “including,” “has,”“having,” “contains” or “containing,” or any other variation thereof,are intended to cover a non-exclusive inclusion. For example, acomposition, a mixture, process, method, article, or apparatus thatcomprises a list of elements is not necessarily limited to only thoseelements but can include other elements not expressly listed or inherentto such composition, mixture, process, method, article, or apparatus.

Additionally, the term “exemplary” is used herein to mean “serving as anexample, instance or illustration.” Any embodiment or design describedherein as “exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments or designs. The terms “at least one”and “one or more” are understood to include any integer number greaterthan or equal to one, i.e. one, two, three, four, etc. The terms “aplurality” are understood to include any integer number greater than orequal to two, i.e. two, three, four, five, etc. The term “connection”can include an indirect “connection” and a direct “connection.”

References in the specification to “one embodiment,” “an embodiment,”“an example embodiment,” etc., indicate that the embodiment describedcan include a particular feature, structure, or characteristic, butevery embodiment may or may not include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to affect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed.

For purposes of the description hereinafter, the terms “upper,” “lower,”“right,” “left,” “vertical,” “horizontal,” “top,” “bottom,” andderivatives thereof shall relate to the described structures andmethods, as oriented in the drawing figures. The terms “overlying,”“atop,” “on top,” “positioned on” or “positioned atop” mean that a firstelement, such as a first structure, is present on a second element, suchas a second structure, wherein intervening elements such as an interfacestructure can be present between the first element and the secondelement. The term “direct contact” means that a first element, such as afirst structure, and a second element, such as a second structure, areconnected without any intermediary conducting, insulating orsemiconductor layers at the interface of the two elements.

The terms “about,” “substantially,” “approximately,” and variationsthereof, are intended to include the degree of error associated withmeasurement of the particular quantity based upon the equipmentavailable at the time of filing the application. For example, “about”can include a range of ±8% or 5%, or 2% of a given value.

The present invention may be a system, a method, and/or a computerprogram product. The computer program product may include a computerreadable storage medium (or media) having computer readable programinstructions thereon for causing a processor to carry out aspects of thepresent invention.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Smalltalk, C++ or the like, andconventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

What is claimed is:
 1. A fluidic device comprising: a first pillar arrayarranged on a substrate, the first pillar array comprising a pluralityof pillars and a plurality of extraction columns, each extraction columncomprising an access opening; and a sealing layer arranged on the firstpillar array to form a sealed fluidic cavity.
 2. The fluidic device ofclaim 1, wherein the fluidic device comprises a deterministic lateraldisplacement (DLD) device.
 3. The fluidic device of claim 1, wherein thesealing layer comprises an oxide.
 4. The fluidic device of claim 1further comprising a second pillar array arranged between the firstpillar array and the sealing layer.
 5. The fluidic device of claim 1,wherein the first pillar array comprises an oxide.
 6. The fluidic deviceof claim 5, wherein the oxide is silicon dioxide.
 7. The fluidic deviceof claim 1, wherein each access opening of each extraction column is asingle slit within a sidewall of the extraction column.
 8. The fluidicdevice of claim 1, wherein each access opening of each extraction columnis three slits within a sidewall of the extraction column.
 9. Thefluidic device of claim 1, wherein each extraction column includes aninverted U-shaped structure.
 10. The fluidic device of claim 9, whereinthe access opening of the inverted U-shaped structure faces thedirection of fluid flow.
 11. A fluidic device comprising: a first pillararray arranged on a substrate, the first pillar array comprising aplurality of pillars and a plurality of extraction columns, eachextraction column comprising an access opening; a sealing layer arrangedon the first pillar array to form a sealed fluidic cavity; and an oxidelayer arranged on the sealing layer, the oxide layer having a pluralityof vent holes aligned over the plurality of extraction columns.
 12. Thefluidic device of claim 11, wherein the fluidic device comprises adeterministic lateral displacement (DLD) device.
 13. The fluidic deviceof claim 11, wherein the sealing layer comprises an oxide.
 14. Thefluidic device of claim 11 further comprising a second pillar arrayarranged between the first pillar array and the sealing layer.
 15. Thefluidic device of claim 11, wherein the first pillar array comprises anoxide.
 16. The fluidic device of claim 15, wherein the oxide is silicondioxide.
 17. The fluidic device of claim 11, wherein each access openingof each extraction column is a single slit within a sidewall of theextraction column.
 18. The fluidic device of claim 11, wherein eachaccess opening of each extraction column is three slits within asidewall of the extraction column.
 19. The fluidic device of claim 11,wherein each extraction column includes an inverted U-shaped structure.20. The fluidic device of claim 19, wherein the access opening of theinverted U-shaped structure faces the direction of fluid flow.